Presently known MOSFET (metal oxide semiconductor field effect transistor) devices incorporate a grown thick field oxide layer which serves to reduce the occurrence of radiation induced field inversion. The undesirable field inversion is known to result in high leakage current with a consequent failure of the MOS circuits. In prior art MOS structures, the oxide layers have a high cross-section for trapping holes generated during irradiation. Radiation may arise from the presence of cosmic rays or nuclear reactions whereby high energy particles penetrate the oxide layers. In such case, the field oxide charges become positive so that the field inverts thereby resulting in parasitic transistor action with high leakage current and device failure.
To solve this problem, dielectric layers, such as undoped oxides deposited by chemical vapor deposition, and also layers using phosphosilicate glass (PSG) oxide were used to reduce the amount of charge trapping. For the manufacture of radiation hard integrated circuits, of the high performance CMOS types for example, it is highly desirable to minimize field inversion and the resultant high leakage current effects so that failure of the MOS circuits will not occur.